<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <canvas id="tutorial" width="300" height="300"></canvas>
  <script>

var ctx;
function draw(){
    var canvas = document.getElementById('tutorial');
    if (!canvas.getContext) return;
    var ctx = canvas.getContext("2d");
 
    ctx.beginPath();
    ctx.arc(20,20, 100, 0, Math.PI * 2);
    ctx.clip();
 
    ctx.fillStyle = "pink";
    ctx.fillRect(20, 20, 100,100);
}
draw();
  </script>
</body>

</html>